The present invention relates generally to the preparation and application of polyurea elastomeric coating/lining systems, and more particularly to a phenolic/polyurea co-polymer system for applications requiring extreme chemical resistance and performance.
Many different types of materials are used to build the engineering structures and vehicles found in our lives today. Most of these materials must be protected from environmental elements of one form or another. For instance, steel needs to be protected from moisture and oxygen to prevent corrosion. Likewise, wood needs to be protected from moisture to prevent rotting. Concrete should be protected from corrosion due to chlorides, other salts, and corrosive air. Further, moisture penetration can lead to spalling of concrete from freeze-thaw cycling.
During the last decade, environmental sensitivity has spawned the need for secondary containment around hazardous chemical storage tanks and processing equipment. Spray polyurea coating systems have become one of the major candidates for secondary containment use. They are used extensively to provide the monolithic impervious membrane to contain spilled and fugitive chemicals caused by leakage or accident.
In addition to the secondary containment of chemicals, surfaces, such as concrete floors, are frequently coated to control dust and dirt that are associated with the substrate when it is not coated. Further, it is often desirable to color code surfaces for pedestrian or worker safety. For instance, roadways have crosswalk striping, and safety railings are often orange or yellow. Identifying danger with a colored coating, and providing barriers to entry or exit are typical of this type of marking.
Many surfaces are coated simply for aesthetic purposes. Even if surfaces need not be protected from the elements, architectural designers commonly specify coatings or other decor to render the completed item artistically pleasing. The color combinations, patterns and decorations they specify are chosen with purpose and careful consideration to have the desired effect.
Paint and coating systems used for these purposes have proliferated over the decades, and polyurea spray elastomeric coating/lining technology has found a place in many of these application areas. Variations of the polyurea technology have allowed for UV color stability, abrasion resistance, easier processing conditions and improved substrate adhesion. U.S. Pat. No. 5,162,388 to Primeaux, II (1992) discloses Aliphatic Polyurea Elastomers comprising an (A) component and a (B) component. The (A) component includes an aliphatic isocyanate, while the (B) component includes an amine-terminated polyoxylalkylene polyol and certain specific cycloaliphatic diamine chain extenders. Primeaux, II (1992) represents one example of a polyurea elastomer system, and in particular, teaches a polyurea elastomer system with good flexibility and ultraviolet stability. U.S. Pat. No. 5,504,181 to Primeaux, II (1996) discloses Aliphatic Spray Polyurea Elastomers comprising an (A) component including an aliphatic isocyanate, and a (B) component including an amine-terminated polyoxyalkylene polyol, and an amine-terminated aliphatic chain extender. The elastomer of Primeaux, II (1996) must be prepared by impingement mixing the isocyanate preparation with the amine-terminated polyether. An additional example of a polyurea elastomer system is found in U.S. Pat. No. 5,480,955, also to Primeaux, II (1996), which teaches additional Aliphatic Spray Polyurea Elastomers. In that reference, the aliphatic spray polyurea elastomer disclosed comprises an (A) component which includes an aliphatic isocyanate, and a (B) component which includes (1) a primary amine-terminated polyoxyalkylene polyol with a molecular weight of at least about 2000, and (2) a specific primary amine-terminated chain extender. A Method of Preparing an Aliphatic Polyurea Spray Elastomer System is disclosed in another patent to Primeaux, II: U.S. Pat. No. 6,013,755. That reference teaches the preparation of a resin blend which is reacted with an isocyanate under conditions effective to form a polyurea elastomer.
The references disclosed herein teach effective methods and materials for coating and protecting a wide variety of substrates. Engineers, however, are always searching for improvements upon earlier inventions, as well as entirely new ones. Two primary deficiencies highly limit the use of polyurea systems in highly chemical/corrosive environments, and in immersion service. The main drawback to the polyurea technology in very corrosive applications is that the resistance to strong acid and base systems, as well as solvents, is very poor. Generally, resistance to crude or heavy fractions of petroleum is excellent, but the ability to withstand the presence of medium to light petroleum fractions is very poor. Solvent resistance also tends to be very selective and highly limited. While the current polyurea technology will withstand relatively low concentrations of acidic and basic solution, exposure to medium to high concentrations tends to result in extreme deterioration and failure in a very short time.
Additionally, the relatively higher moisture vapor permeation through the coating system allows for its delamination from certain substrates in immersion/lining applications. This problem is common in steel tank lining applications where you have a temperature gradient from inside the tank to the outside. In other words, the liquid inside the tank is heated and the ambient temperature outside the tank is relatively cooler. This results in a moisture drive through the coating/lining system and causes a phenomenon referred to as xe2x80x9cCold Wall Effect.xe2x80x9d
The present invention is directed to one or more of the problems or shortcomings associated with the prior art.
The present invention address one or more of the deficiencies noted above with respect to the current polyurea spray elastomer coating/lining technology. This invention will markedly improve the performance of the polyurea elastomer coating/lining technology with regard to both moisture vapor transmission and chemical resistance.
A primary aspect of the present invention is the reacting of phenolic resins, blended into the resin blend component, with polyisocyanates in the polyurea formulation. The incorporation of the phenolic resins into the polyurea backbone will increase cross-link density of the cured polymer, resulting in a reduction of the moisture vapor transmission compared to non-phenolic containing polyurea system.
Phenolics are also known for their chemical resistance, and it is therefore expected that the inclusion of phenolic resins will enhance the chemical resistance of cured systems. Phenolics are also known for high temperature resistance, making another benefit of phenolic inclusion an increased elevated temperature resistance over non-phenolic systems. Phenolics are also known for their superior adhesion characteristics compared to other materials. The use of phenolic resins in the polyurea technology will tend to improve adhesion to the various substrates that are coated/lined, and give significant performance advantages over the current polyurea elastomer coating/lining technology.
To complement the above, specialized epoxy resins may be incorporated to form an Interpenetrating Polymer Network, further enhancing the target properties of the present invention.
The present invention relates to the preparation and application of plural component, phenolic/polyurea co-polymer coating systems that exhibit significantly improved chemical resistance as compared to conventional polyurea elastomer coating systems. The present systems include the reaction product of two components to produce a phenolic/polyurea co-polymer elastomeric coating system. In the preferred embodiment, the first, (a), component comprises an isocyanate, and preferably includes an isocyanate quasi-prepolymer of an isocyanate and an active hydrogen containing material. The second, (b), component comprises a resin blend of an active amine hydrogen containing material, which is preferably an amine-terminated polyether, and a phenolic resin. In the preferred embodiment, component (b) also includes a chain extender, although it should be appreciated that an elastomer could be developed that did not incorporate a chain extender without departing from the spirit and scope of the present invention. Because the phenolic-based resins are also an active hydrogen containing material, they may also be utilized in preparation of the isocyanate quasi-prepolymer. The phenolic resin is preferably introduced during the preparation/blending of the co-polymer system components.
Examples of amine terminated polyethers, isocyanates, and chain extenders that can be used in accordance with the present invention are those well known in the polyurea art as described in U.S. Pat. Nos. 4,891,086; 5,013,813; 5,082,917; 5,153,232; 5,162,388; 5,171,819; 5,189,075; 5,218,005; 5,266,671; 5,317,076; 5,442,034; 5,480,955; 5,504,181; 5,616,677; and 6,013,755, all incorporated herein by reference. It should be understood that other materials, in addition to those listed in the aforementioned patents, might be used without departing from the scope of the present invention.
The active amine hydrogen containing materials employed in the present invention are preferably amine-terminated polyethers. However, the use of high molecular weight amine-terminated alkylenes, simple alkyl amines, and other suitable amine-terminated materials with varying molecular weights and chemical compositions are contemplated by the present invention, and could be used alone or in combination with other suitable materials without departing from its intended scope. The term xe2x80x9chigh molecular weight,xe2x80x9d is intended to include polyether amines having a molecular weight of at least about 1,500. The preferred amine-terminated polyethers should be selected from aminated diols or triols, and a blend of aminated diols and/or triols is most desirable. The amine-terminated polyethers are preferably selected from mixtures of high molecular weight polyols, such as mixtures of di- and trifunctional materials. In particular, primary and secondary amine-terminated polyethers with a molecular weight greater than 1500, even more desirably greater than 2000, a functionality from about 2 to about 6, and an amine equivalent weight of from about 750 to about 4000 are preferred. In the preferred embodiment, such amine-terminated polyethers having a functionality of from about 2 to about 3 are used. These materials may be made by various methods known in the art. It is not necessary that a blend of polyethers be used, and it should be appreciated that a single high molecular weight aminated polyol might be used without departing from the scope of the present invention.
The amine-terminated polyethers preferred in the instant invention may be, for example, polyether resins made from an appropriate initiator to which lower alkylene oxides, such as ethylene oxide, propylene oxide, butylene oxide, or mixtures thereof, are added with the resulting hydroxyl-terminated polyol then being aminated. When two or more oxides are used, they may be present as random mixtures or as blocks of one or the other polyether. In the amination step, it is highly desirable that the terminal hydroxyl groups in the polyol be essentially all secondary hydroxyl groups for ease of amination. The polyols so prepared are then reductively aminated by known techniques, such as described in U.S. Pat. No. 3,654,370, for example, the contents of which are incorporated herein by reference. Normally, the amination step does not completely replace all of the hydroxyl groups. However, the greatest majority of hydroxyl groups are replaced by amine groups. Therefore, in a preferred embodiment, the amine-terminated polyether resins useful in this invention have greater than about 90 percent of their active hydrogens in the form of amine hydrogens.
Particularly noted are the JEFFAMINE(copyright) brand series of polyether amines available from Huntsman Corporation. They include JEFFAMINE(copyright) D-2000, JEFFAMINE(copyright) D-4000, JEFFAMINE(copyright) T-3000 and JEFFAMINE(copyright) T-5000. These polyetheramines are described with particularity in Huntsman Corporation""s product brochure entitled xe2x80x9cThe JEFFAMINE(copyright) Polyoxyalkyleneaminesxe2x80x9d. Other similar polyether amines are commercially available from BASF and Arch Chemicals.
Both aromatic and aliphatic isocyanates can be used in the present invention, and the preferred aliphatic isocyanates include those known to one skilled in the polyurea elastomer art. Thus, for instance, the aliphatic isocyanates are of the type described in U.S. Pat. No. 5,162,388, the contents of which are incorporated herein by reference. They are typically aliphatic diisocyanates and are preferably the bifunctional monomer of the tetraalkyl xylene diisocyanate, such as the tetramethyl xylene diisocyanate, or the trimerized or the biuret form of an aliphatic diisocyanate, such as hexamethylene diisocyanate. In addition, cylcohexane diisocyanate and isophorone diisocyanate are considered preferred aliphatic isocyanates. Other useful aliphatic polyisocyanates are described in U.S. Pat. No. 4,705,814, which is incorporated herein by reference. The aforementioned isocyanates can be used alone or in combination.
A wide variety of aromatic isocyanates, preferably polyisocyanates, can also be utilized to produce the polyurea elastomer that is the object of the present invention. Typical aromatic polyisocyanates include p-phenylene diisocyanate, polymethylene polyphenyl-isocyanate, 2,6-toluene diisocyanate, 2,4-toluene diisocyanate, naphthalene-1,4-diisocyanate, bis-(4-isocyanatophenyl)methane, and bis-(3-methyl-4-isocyanatophenyl)methane. Other aromatic isocyanates used in the practice of this invention are methylene-bridged polyphenyl polyisocyanate mixtures which have functionalities of from about 2 to about 4. These aromatic isocyanates are well described in the literature and in many patents, for example, U.S. Pat. Nos. 2,683,730; 2,950,263; 3,012,008; 3,344,162; and 3,362,979, all incorporated herein by reference.
Usually methylene-bridged polyphenyl polyisocyanate mixtures contain from about 20 to about 100 wt % methylene diphenyl diisocyanate isomers, with the remainder being polymethylene polyphenyl diisocyanate having higher functionalities and higher molecular weights. Typical of these are polyphenyl polyisocyanate mixtures containing from about 20 to about 100 wt % diphenyldiisocyanate isomers, of which from about 20 to about 95 wt % thereof is the 4,4xe2x80x2-isomer with the remainder being polymethylene polyphenyl polyisocyanates of higher molecular weight and functionality that have an average functionality of from about 2.1 to about 3.5. These isocyanate mixtures are known, commercially available materials and may be prepared by the process described in U.S. Pat. No. 3,362,979.
By far the most preferred aromatic polyisocyanate is methylene bis(4-phenylisocyanate) or xe2x80x9cMDIxe2x80x9d. Pure MDI, quasi-prepolymers of MDI, and modified pure MDI, etc., are useful. Materials of this type may be used to prepare suitable elastomers. Since pure MDI is a solid and, thus, inconvenient to use, liquid products based on MDI are also disclosed herein. For example, U.S. Pat. No. 3,394,164, which is incorporated herein as reference, describes a liquid MDI product. More generally, uretonimine modified pure MDI is also included. This product is made by heating pure distilled MDI in the presence of a catalyst. Examples of commercial materials of this type are ISONATE(copyright) 125M (pure MDI) and ISONATE(copyright) 2143L, RUBINATE(copyright) 1680, RUBINATE(copyright) 1209 and MONDUR(copyright) ML (xe2x80x9cliquidxe2x80x9d MDIs). The ISONATE(copyright) products are available from Dow Chemical, the RUBINATE(copyright) products are available from Huntsman Polyurethanes and the MONDUR products available from Bayer Corporation.
Preferably, the amount of isocyanate used to produce the present polyurea elastomers is equal to or greater than the stoichiometric amount based on the active hydrogen ingredients in the formulation. The ratio of equivalents of isocyanate groups in the polyisocyanate to the active hydrogens, preferably amine hydrogens, is in the range of 0.95:1 to about 2.00:1, with about 1.00:1 to about 1.50:1 being preferred and about 1.05:1 to about 1.30:1 being most preferred. This ratio is sometimes referred to as the isocyanate INDEX and is expressed as a percentage of excess isocyanate. The isocyanate INDEX compares the total isocyanate with the total active hydrogen in the reactant compounds.
It should be understood that the term xe2x80x9cisocyanatexe2x80x9d also includes quasi-prepolymers of isocyanates with active hydrogen-containing materials. The active hydrogen-containing materials used to prepare a prepolymer can include a polyol or a high molecular weight amine-terminated polyether, also described herein as amine terminated alkylenes, or a combination of these materials. The amine-terminated polyethers useful in preparing quasi-prepolymers of isocyanate include the same amine-terminated polyethers described herein as amine-terminated materials for producing polyureas.
The isocyanate quasi-prepolymer of component (a) is preferably prepared from an active hydrogen containing material selected from the group consisting of polyols, amine-terminated alkylenes, and blends thereof. The polyols used in preparing a quasi-prepolymer preferably include polyether polyols, polyester diols, triols, etc., should have an equivalent weight of at least 500, and more preferably at least about 1,000 to about 5,000. In particular, those polyether polyols based on trihydric initiators of about 4,000 molecular weight and above are especially preferred. The polyethers may be prepared from ethylene oxide, propylene oxide, butylene oxide or mixture of propylene oxide, butylene oxide and/or ethylene oxide. Other high molecular weight polyols that may be useful in this invention are polyesters of hydroxyl-terminated rubbers, e.g., hydroxyl terminated polybutadiene. Quasi-prepolymers prepared from hydroxyl-terminated polyols and isocyanates are generally reserved for use with aromatic polyurea spray systems.
Isocyanate quasi-prepolymers are also available commercially prepared. These are based on different types of MDI monomers and a variety of polyether and polyester polyols. These products are sold under the various trade names of: RUBINATE 9009, RUBINATE 9495, RUBINATE 9484, RUBINATE 9480, and RUBINATE 9272, all from Huntsman Polyurethanes; MONDUR 1453 and MONDUR 1437 form Bayer Corporation.
U.S. Pat. No. 5,442,034, incorporated herein by reference, teaches one that alkylene carbonates may be incorporated in the isocyanate quasi-prepolymer for improved mixing characteristics of the polyurea elastomer system. The preferred alkylene carbonates used in the present invention include ethylene carbonate, propylene carbonate, butylene carbonate and dimethyl carbonate, or mixtures thereof.
The present polyurea elastomer systems may also comprise an amine-terminated chain extender. The aromatic chain extenders preferably used in the present invention include many amine-terminated aromatic chain extenders that are well known to the polyurea art. Typical aromatic chain extenders include, for example, 1-methyl-3,5-diethyl-2,4-diaminobenzene, 1-methyl-3,5-diethyl-2,6-diaminobenzene (both referred to as diethyltoluene diamine or DETDA and are commercially available form Albemarle), 1,3,5-triethyl-2,6-diaminobenzene, 3,5,3xe2x80x2,5xe2x80x2-tetraethyl-4,4xe2x80x2-diaminodiphenylmethane and the like. Particularly preferred aromatic diamine chain extenders are 1-methyl-3,5-diethyl-2,4-diaminobenzene or a mixture of this compound with 1-methyl-3,5-diethyl-2,6-diaminobenzene. Other useful aromatic chain extenders include, but are not limited to, di(methylthio)toluene diamine or N,Nxe2x80x2-bis(sec-butyl)methylenedianiline, each of which can be used alone or, preferably, in combination with 1-methyl-3,5-diethyl-2,4-diaminobenzene or 1-methyl-3,5-diethyl-2,6-diaminobenzene. This combination includes from about 20 to about 99 parts of di(methylthio)toluene diamine of N,Nxe2x80x2-bis(sec-butyl)methylenedianiline to about 80 to about 1 parts DETDA.
Other examples of useful chain extenders include low molecular weight amine-terminated polyethers, including primary and secondary amine-terminated polyethers of less than 400 molecular weight, having a functionality of from about 2 to about 6, preferably from about 2 to about 4. In addition, low molecular weight amine-terminated alkylenes and simple alkyl amines are included within the scope of this invention, and may be used alone or in combination with the aforementioned amine-terminated polyols. In addition, other amine-terminated materials having different molecular weight or different chemical compositions may be used. The term xe2x80x9clow molecular weightxe2x80x9d is intended to include polyether amines having a molecular weight of less than 400. Although the chain extenders used in the present invention are preferably amine-terminated chain extenders, they need not be amine-terminated materials at all. Alternatives include low molecular weight hydroxyl-terminated polyethers, having a functionality of from about 2 to about 6, preferably from about 2 to about 4. These include, but are not limited to, ethylene glycol, propylene glycol, glycerin and 1,4-butanediol.
The preferred phenolic resins used in the instant invention are those that have an active hydrogen content of equal to or greater than 2. In other words, a hydroxyl functionality of greater than or equal to 2. Mono-functional phenolic resins are not preferred, because they are likely to lead to polymer chain termination, potentially severely affecting elastomer physical properties and performance. Examples of useful phenolic resins are ARYLFLEX(copyright) DS, a di-functional resin, and ARYLFLEX M4P, a tetra-functional resin. Both products are available from Lyondell Chemical. The use of such phenolic resins in a single component, moisture-cure polyurethane application is taught in U.S. Pat. No. 6,245,877.
The polyurea elastomers of the present invention are characterized by urea linkages formed by the reaction of active amine hydrogen groups with isocyanates. However, some of the active hydrogen groups in the reaction mixture are in the form of hydroxyl groups in the phenolic resins. Thus, the polyurea elastomers referred to herein are those formed from reaction mixtures having at least about 70 percent of the active hydrogen groups in the form of amine groups. Preferably, the reaction mixtures have at least about 80 percent of the active hydrogen groups in the form of amine groups, and even more preferably, the reaction mixtures have at least 85 percent of the active hydrogen groups in the form of amine groups.
Another component that may be included as part of the present elastomer system is an epoxy resin. Epoxy resins tend to react with active hydrogens on amine functional materials, forming the basis of the epoxy reaction/curing mechanism. For this reason, the epoxy resin is preferably not incorporated into the active amine hydrogen resin blend component (b). Many epoxy resins also tend to react with isocyanate components making incorporation into the isocyanate side of the disclosed coating system also difficult. By using specially modified epoxy resins, they may be included in the isocyanate side of the coating system without any problem. Once this component is mixed with the resin blend component of the disclosed system, the epoxy resins can react with the active amine hydrogens to form an Interpenetrating Polymer Network. This tends to further improve chemical resistance, lower moisture vapor transmission and possibly improves substrate adhesion. These epoxy resins are preferably based on cyclohexanedimethanol diglycidyl ethers and supplied as ERISYS GE-22 and ERISYS GE-22S from CVC Specialty Chemicals.
Pigments, for example, titanium dioxide and/or carbon black, may also be incorporated in the elastomer system to impart color properties. Pigments may be in the form of solids or the solids may be pre-dispersed in a resin carrier. Reinforcements, for example, flake or milled glass, and fumed silica, may also be incorporated in the elastomer system to impart certain properties. Other additives such as UV stabilizers, antioxidants, air release agents, adhesion promoters, or structural reinforcing agents may be added to the mixture depending on the desired characteristics of the end product. These are generally known to those skilled in the art.
Preferably, the phenolic/polyurea co-polymer coating/lining systems of the present invention are prepared using plural component, high pressure, high temperature spray equipment. As known in the art, plural component equipment combines two components, an (a) component and a (b) component. The (a) component generally includes an isocyanate material, while the (b) component generally includes the amine terminated polyethers and phenolic resins. Other additives may also be included in the resin blend component as noted previously. The (a) component and the (b) component of the phenolic/polyurea co-polymer system are preferably combined or mixed under high pressure. In a preferred embodiment, they are impingement mixed directly in the high-pressure spray equipment. This equipment for example includes: GUSMER H-2000, GUSMER H-3500, GUSMER H-20/35 and Glas-Craft MH type proportioning units fitted with either a GUSMER GX-7, GUSMER GX-7 400 series or GUSMER GX-8 impingement mix spray gun. The two components are mixed under high pressure inside the spray gun thus forming the coating/lining system, which is then applied to the desired substrate via the spray gun. The use of plural component spray equipment, however, is not critical to the present invention and is included only as one example of a suitable method for mixing the phenolic/polyurea co-polymer systems of the present invention.
A further advantage of the present invention is that the phenolic/polyurea co-polymer reactants discussed herein can react to form the present phenolic/polyurea co-polymer elastomer system without the aid of a catalyst. Catalysts may be used in the normal preparation of the isocyanate quasi-prepolymer. Therefore, the catalyst may be excluded during the practice of this invention in the preparation of the plural component, phenolic/polyurea co-polymer elastomer system.
Post curing of the phenolic/polyurea co-polymer elastomeric system is optional. Post curing will improve certain elastomeric properties, and use depends on the desired properties of the end product. Post curing may be used as a tool to speed up the final cure of the phenolic/polyurea co-polymer to allow for rapid elastomer properties evaluation.
As a result of the improved chemical resistance, lower moisture vapor transmission and substrate adhesion of the phenolic/polyurea co-polymer systems, the present invention produces excellent candidate materials for coating/lining applications of substrates such as concrete, steel, aluminum, glass, fiberglass, pressed wood oriented strand board, asphalt, thermoplastic polymers of polyethylene and polypropylene, expanded polystyrene, polyurethane foam, sealants and goetextile fabrics. The fast cure time of the systems of the present invention will allow for rapid turn around time for the coating/application work. This could include steel tank lining, concrete tank linings, sewage and waste-water lift stations, pipe linings, secondary containment, roof coating, bedliners, road marking coatings, traffic deck coatings and off-shore corrosion protection in the refining and maritime industry.
It should be understood that the present description is for illustrative purposes only and should not be construed to limit the scope of the present invention in any way. Thus, those skilled in art will appreciate that various modifications and alterations to the presently disclosed embodiments might be made without departing from the intended spirit and scope of the present invention. Additional advantages and details of the present invention are evident upon an examination of the following examples and appended claims.